Method of forming a composite containing a matrix component and at least one liquid crystal component

ABSTRACT

A method of forming a composite containing a matrix component and at least one liquid crystal component includes providing a matrix, providing a first material that is phase separable from the matrix, adding the first material to the matrix, and replacing the first material that is phase separable form the matrix with a second material exhibiting liquid crystalline behavior.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/498,166, filed Jun. 9, 2004, the entire contents of which areincorporated herein by reference. U.S. application Ser. No. 10/498,166is National Stage of International application PCT/EP02/14243 filed Dec.13, 2002, and claims the benefit of priority under 35 U.S.C. §119 fromEuropean Application No. EP 01 129 709.0 filed Dec. 13, 2001.

The present invention relates to a method of forming a compositecontaining a matrix component and at least one liquid crystal component.It also relates to a composite obtainable thereby, and to uses thereof.

Ever since it was first demonstrated, in 1976, that it was possible tochange a liquid crystal composite from an opaque to a transparent state,a tremendous amount of research effort has been invested to achieveprogress and to adapt this phenomenon for use in electronic componentsetc. The principle of changing a liquid crystal from an opaque to atransparent state was applied to a porous polymer matrix (Craighead etal., 1982, Appl. Phys. Lett. 40, 22), which was filled with a liquidcrystal. The idea of encompassing a liquid crystal within a matrix,which in Craighead's experiments showed a poor performance, was furtherdeveloped in 1985 by Fergason (1985, SID Int. Symp. Digest of Tech.Papers, 16, 68) and Drzaic, (1986, J. Appl. Phys., 60, 2142) whoreported liquid crystal-polymer composites obtained by drying anemulsion of liquid crystal in an aqueous solution of polyvinyl alcohol.These materials were termed “nematic curvilinear aligned phase” (NCAP)which found use in smart window applications. In NCAP applications theliquid crystal is encapsulated by standard microencapsulation oremulsification techniques which suspend it in a solid polymer film.

Another technique which was developed on the basis of Craighead's ideato embed the liquid crystal in a polymer matrix, is the so calledPDLC-technique (polymer-dispersed liquid crystal). This is achieved bypreparing a homogeneous mixture of a liquid crystal and a pre-polymerand thereafter inducing a phase separation by causing the pre-polymer toform a solid network, thereby inducing the liquid crystal form dropletsembedded in the polymer network. Various techniques have been developedto achieve such formation of a polymer network which are used dependingon the individual circumstances. For example, when a pre-polymermaterial is miscible with a liquid crystal compound a phase separationby polymerization is used. This technique is referred to aspolymerization-induced phase separation (PIPS). A homogeneous solutionis made by mixing the pre-polymer with the liquid crystal. Thereafter apolymerization is achieved through a condensation reaction, as withepoxy resins, or through a free radical polymerization, as with vinylmonomer catalyzed with a free radical initiator such as benzoylperoxide, or by a photo-initiated polymerization. Upon polymerizationthe solubility of the liquid crystal decreases in the lengtheningpolymers until the liquid crystal forms droplets or an interconnectedliquid crystal network within a growing polymer network. When thepolymer starts to gel it will lock the growing droplets or theinterconnected liquid crystal network thereby arresting them/it intheir/its state at that time. The droplet size and the morphology ofdroplets or the dimensions of the liquid crystal network are determinedduring the time between the droplet nucleation/initiation of networkformation and the gelling of the polymer. Important factors are the rateof polymerization, the relative concentrations of materials, thetemperature, the types of liquid crystal and polymers used and variousother physical parameters, such as viscosity, solubility of the liquidcrystal in the polymer. Reasonably uniform size droplets can be achievedby this technique. Sizes prepared in the past have ranged from 0.01μm-30 μm. Polymerisation induced phase separation (PIPS) is a preferredmethod for forming PDLC films. The process begins with a homogeneousmixture of liquid crystal and monomer or pre-polymer. Polymerisation isinitiated to induce phase separation. Droplet size and morphology aredetermined by the rate and the duration of polymerisation, the types ofliquid crystal and polymers and their proportions in the mixture,viscosity, rate of diffusion, temperature and solubility of the liquidcrystal in the polymer (West, J. L., Phase-separation of liquid-crystalsin polymer. Molecular Crystals and Liquid Crystals, 1988. 157: p.427-441, Golemme, A., Zumer, S., Doane, J. W., and Neubert, M. E.,Deuterium nmr of polymer dispersed liquid crystals. Physical Review a,1988. 37(2): p. 599-569, Smith, G. W. and Vaz, N. A., The relationshipbetween formation kinetics and microdroplet size of epoxy basedpolymer-dispersed liquid-crystals. Liquid Crystals, 1988. 3(5): p.543-571, Vaz, N. A. and Montgomery, G. P., Refractive-indexes ofpolymer-dispersed liquid-crystal film materials epoxy based system.Journal Of Applied Physics, 1987. 62(8): p 3161-3172). In ultravioletlight (UV) initiated polymerisation, the rate of curing may be changedby changing the light intensity (Whitehead Jr, J. B., Gill, N. L., andAdams, C., Characterization of the phase separation of the E7 liquidcrystal component mixtures in a thiol-ene based polymer. Proc. SPIE,2000. 4107: p. 189). The PIPS method using free-radical polymerisationis by far the most studied, and the majority of free-radicalpolymerisation systems are initiated by UV light. The process hasseveral advantages over other methods such as, better phase separation,uniform droplet size, and better control of the droplet size. However,the presence of dyes that absorb UV and visible radiation in the mixtureprior to curing can lead to incomplete or the complete prevention ofsuccessful curing. Furthermore, the dyes may decompose upon curing.

Another technique used for obtaining PDLC composites is thermal inducedphase separation (TIPS). This technique can be used for liquid crystalmaterials and thermoplastic materials which are capable of forming ahomogenous solution above the melt temperature of the polymer. Thehomogenous solution of liquid crystal in the thermoplastic melt iscooled below the melting point of the thermoplastic material, therebycausing a phase separation of the liquid crystal. The droplet size ofthe liquid crystal is determined by the rate of cooling and a number ofother material parameters. Examples of TIPS-prepared composites arepolymethylmethacrylate (PMMA) and polyvinylformal (PVF) withcyanobiphenyl liquid crystal. Generally, the concentrations of liquidcrystals required for TIPS-film are larger in comparison toPIPS-prepared films.

Another technique used to prepare polymer dispersed liquid crystalcomposites is solvent-induced phase separation (SIPS). This makes use ofa liquid crystal and a thermoplastic material dissolved in a commonsolvent thereby forming a homogenous solution. The ensuing evaporationof the solvent results in phase separation of the liquid crystal,droplet formation and growth, and polymer gelation. Solvent evaporationcan also be used in conjunction with thermal processing of materialswhich melt below their decomposition temperature. First of all films areformed on a suitable substrate using standard film coating techniques,e.g. doctor blading, spin coating, web coating, etc. The solvent isthereafter removed with no concern of droplets size or density. Then thefilm is warmed again to re-dissolve the liquid crystal in the polymerand then cooled at a rate which is chosen to give the desired dropletsize and density. In effect, the latter example is a combination of SIPSwith TIPS.

A common problem encountered with all of these aforementioned techniquesis the fact that the phase-separation achieved is only incomplete, i.e.some of the liquid crystal plasticizes the polymer network formed,because it stays co-dissolved within the polymer. This isdisadvantageous for any electronic device making use of such liquidcrystal.

Electronic device display technologies require displays with highbrightness and contrast, low power consumption, and fast refresh speeds.For flexible displays, polymer thin film technology is being exploredand in particular, polymer dispersed liquid crystal films (=PDLC) are ofinterest. In these materials it is important to achieve good phaseseparation of the components with minimal co-dissolution. Suchco-dissolution reduces the scattering-switching contrast between “on”and “off” states. Furthermore, if coloured dyes are used to producecoloured PDLC films, dissolution of the dye into the inactive polymermatrix reduces colour-switching contrast. An additional impediment isthat in the preferred curing method, that of ultra-violet light photocuring, many coloured dyes undergo photodegradation. There are otheradvantages which would make it appear desirable to add dyes to PDLCcomposite films. Addition of dipolar dyes can, for example lead tofaster “turn-on” times.

Another problem commonly encountered with PDLC composites is the factthat additional components dissolved in the liquid crystal are sensitiveto the phase separation process and frequently are damaged in the courseof the polymerization and/or the formation of the polymer matrix. Forexample it is very difficult to include UV-sensitive dyes which survivephotoinduced polymerization. Accordingly it has been a problem toproduce PDLC-composites which are coloured by the inclusion of dyes.

Therefore it has been an object of the present invention to avoidco-dissolution of the liquid crystal component, damaging of additionalcomponents by conditions associated with polymer formation etc. and theother problems associated with the prior art.

It has further been an object to provide polymer dispersed liquidcrystal composites which are useful for colour application and/or have abetter performance.

The object of the invention is solved in a first aspect by method offorming a composite containing a matrix component and at least oneliquid crystal component, comprising the following steps:

-   -   a) providing a matrix,    -   b) providing a first material that is phase separable from the        matrix,    -   c) adding the first material to the matrix,    -   d) adding a second material exhibiting liquid crystalline        behaviour to the matrix.

Preferably, the method according to the present invention comprises asstep d): replacing the first material that is phase separable from thematrix with a second material exhibiting liquid crystalline behaviour.

In a preferred embodiment the first material exhibits liquid crystallinebehaviour. In one embodiment the first material is liquid.

Preferably, the first material is selected from the group comprisingwater, aqueous solutions, aqueous suspensions, aqueous emulsions andoils.

It is preferred that the matrix is a polymer-matrix.

Preferably the matrix is porous.

The term “porous” as used herein is meant to signify that the matrixprovides an interstitial space wherein other matter can be taken up,e.g. liquids. Preferred embodiments of a matrix according to the presentinvention are sponges, filters, filter papers, gels, networks, sieves,polymer gels, polymer sieves.

Further examples of the matrix are inorganic networks, e.g. silicanetworks, which can for example be produced by a sol-gel process, orxerogels. The latter term applies to any very low-density network wherethere is a continuous void phase and where there is a solid phase thatis either of an organic or inorganic material.

In a preferred embodiment the interstitial space has dimensions in thex, y, z-directions taken from the range 100 nm-30 μm, more preferably500 nm-10 μm and even more preferably 600 nm-5 μm. Most preferably theinterstitial space's dimensions (pore size) are centered around 3 μm.

The idea of these dimensions is, that, although this is not absolutelyessential to the invention, scattering of electromagnetic radiationshall be achieved by appropriate choice of dimensions. Without wishingto be bound by any particular theory, the inventors have found that bychoosing the aforementioned dimensions, scattering can be achieved andthereby the absorption of electromagnetic radiation through dyes,possibly included in the liquid crystalline phase, can be enhanced,because the pathlength of light has been increased.

Preferably, the maximum refractive index difference between the matrixand the liquid crystal material is >0.01, in order to achievescattering.

The term “phase separable” is meant to designate the fact that where amaterial is denoted as “phase separable” from the matrix etc. it can beseparated therefrom due to it having a phase different to the phase ofthe matrix etc., i.e. the phase is the separating criterion.

Preferably, the first material exhibiting liquid crystalline behaviouris the same as the second material exhibiting liquid crystallinebehaviour.

In another embodiment, the first material exhibiting liquid crystallinebehaviour is different to the second material exhibiting liquidcrystalline behaviour.

It is preferred that the second material exhibiting liquid crystallinebehaviour contains at least one additional component, which, preferably,is soluble in the second material.

More preferably, the soluble component is selected from the groupcomprising dyes, compounds with permanent dipoles, rod-like structurematerials, nanotubes.

In one embodiment, the soluble component is selected from the groupcomprising UV-sensitive dyes, UV-stable dyes, cis-trans isomer dyes,dichroic dyes and dipolar dyes.

Preferably, the composite after d) is heated above the isotropictemperature of the second material, wherein, more preferably, theheating is above the isotropic temperature of the second material, butbelow the decomposition temperature/melting temperature of the matrix.

In a second preferred aspect, the object is solved by a method offorming a composite containing at least one polymer component and atleast one liquid crystal component, comprising the following steps:

-   -   a) providing a material capable of forming a solid polymer,    -   b) providing a material that is phase separable from the solid        polymer,    -   c) inducing the material capable of forming a solid polymer, to        form a solid polymer,    -   d) adding a liquid crystal material.

Preferably, the material that is phase separable from the solid polymeris selected from the group comprising water, aqueous solutions, aqueoussuspensions, aqueous emulsions and oils.

In a preferred embodiment, the material that is phase separable from thesolid polymer is a liquid crystal material.

In one embodiment, the liquid crystal material of step d) is the same asthe liquid crystal material that is phase separable from the solidpolymer.

In another embodiment, the liquid crystal material of step d) isdifferent to the liquid crystal material that is phase separable fromthe solid polymer.

Preferably, the liquid crystal material of step d) contains at least oneadditional component.

It is preferred that the at least one additional component is soluble inthe liquid crystal material, wherein, preferably, the soluble componentis selected from the group comprising dyes, compounds with permanentdipoles, rod-like structure materials, nanotubes.

More preferably, the soluble component is selected from the groupcomprising UV-sensitive dyes, UV-stable dyes, cis-trans isomer dyes,dichroic dyes and dipolar dyes.

In a preferred embodiment, step d) comprises the following substep

-   da): removing the liquid crystal material that is phase separable    from the solid polymer, by a process selected from the group    comprising washing out, evaporation and suction.

It is to be understood that the removal of the liquid crystal materialthat is phase separable from the solid polymer and the addition of theliquid crystal material of step d) may be serial or concomitant.

In one embodiment, in step d) the liquid crystal material is added tothe mixture by a process selected from imbibing the liquid crystalmaterial into the solid polymer, flooding the solid polymer with theliquid crystal material, immersing the solid polymer into the liquidcrystal material, capillary force filling the solid polymer undervacuum.

Preferably, in step c) a polymer dispersed liquid crystal pre-compositeis formed by a phase separation process.

It is preferred that the phase separation process is selected from thegroup comprising thermally-induced phase separation (TIPS),solvent-induced phase separation (SIPS) and polymerization-induced phaseseparation (PIPS).

Preferably, the composite after d) is heated above the isotropictemperature of the liquid crystal material of step d), wherein, morepreferably, the heating is above the isotropic temperature of the liquidcrystal material of step d), but below the decompositiontemperature/melting temperature of the solid polymer.

In a third preferred aspect the object of the present invention issolved by a method of forming a composite containing at least onepolymer component and at least one liquid crystal component, comprisingthe following steps:

-   a) providing a material, containing polymer precursors,-   b) providing a first liquid crystal material,-   c) mixing the material, containing polymer precursors, and the    liquid crystal material to form a mixture,-   d) inducing the material, containing polymer precursors, to undergo    a polymerization reaction,-   e) adding a second liquid crystal material to the mixture.

In one embodiment, the second liquid crystal material is the same as thefirst liquid crystal material, wherein, preferably, the second liquidcrystal material is different to the first liquid crystal material.

It is preferred that the second liquid crystal material contains atleast one additional component, wherein, preferably, the at least oneadditional component is soluble in the second liquid crystal materialand the first liquid crystal material, or in the second liquid crystalmaterial only.

In one embodiment, the additional component, which is soluble in thesecond liquid crystal material and the first liquid crystal material, orin the second liquid crystal material only, is selected from the groupcomprising dyes, compounds with permanent dipoles, rod-like structurematerials and nanotubes.

Preferably, the soluble component is selected from the group comprisingUV-sensitive dyes, UV-stable dyes, cis-trans isomer dyes, dipolar dyesand dichroic dyes.

In one embodiment, step e) comprises the following substep

-   ea): removing the first liquid crystal material from the mixture by    a process selected from the group comprising washing out,    evaporation and suction.

Preferably, in step e) the second liquid crystal material is added tothe mixture by a process selected from imbibing the liquid crystalmaterial into the mixture, flooding the mixture with the liquid crystalmaterial, immersing the mixture into the liquid crystal material andcapillary force filling the mixture under vacuum.

Preferably, the composite after e) is heated above the isotropictemperature of the second liquid crystal material, wherein, morepreferably, the heating is above the isotropic temperature of the secondliquid crystal material, but below the decomposition temperature/meltingtemperature of the polymer formed in d).

It is to be understood that the removal of the first liquid crystalmaterial and the addition of the second liquid crystal material may beserial or concomitant.

In a fourth aspect, the object of the invention is also solved by acomposite obtainable by a method according to the present invention,wherein, preferably, the composite contains a liquid crystal componentdoped with a compound selected from the group comprising dyes,UV-sensitive dyes, UV-stable dyes, dichroic dyes, dyes with a permanentdipole, rod-like structure material and nanotubes.

In a preferred embodiment, the composite is characterized by thefollowing features: T_(max) and T_(min) having ranges of from 0-100%,V₁₀, V₉₀ and V_(sat) having ranges of from 0->100V, wherein, preferably,T_(max) has a range of from 80˜100%, T_(min) has a range of from 0˜30%,V₁₀ has a range of from 0˜5V, V₉₀ has a range of from 5˜20 V,Absorption_(on) has a range of from 0.05˜0.10, and Absorption_(off) hasa range of from 0.90˜1.00.

In a fifth aspect, the object of the present invention is also solved bya composite containing at least one solid polymer component and at leastone liquid crystal component, characterized in that it contains a liquidcrystal component doped with a compound selected from the groupcomprising dyes, UV-sensitive dyes, UV-stable dyes, dichroic dyes, dyeswith a permanent dipole, rod-like structure materials and nanotubes.

Preferably, the composite is characterized by the following features:T_(max) and T_(min) having ranges of from 0-100%, V₁₀, V₉₀ and V_(sat)having ranges of from 0->100V, wherein, more preferably, T_(max) has arange of from 80˜100%, T_(min) has a range of from 0˜30%, V₁₀ has arange of from 0˜5V, V₉₀ has a range of from 5˜20 V, Absorption_(ON)(A_(ON)) has a range of from 0.05˜0.10, Absorption_(OFF) (A_(OFF)) has arange of from 0.90˜1.00, and/or the contrast ratio A_(OFF)/A_(ON) has arange of from 6˜20.

The values for T_(max), T_(min), V₁₀, V₉₀, V_(sat) are dependent on thesample and the cure conditions and vary from 0˜100% (T_(max), T_(min)),and from 0˜>100V (V₁₀, V₉₀, V_(sat)).

In a sixth aspect, the object is furthermore solved by a compositecontaining at least one solid polymer component and at least one liquidcrystal component, characterized by the following features: T_(max) andT_(min) having ranges of from 0-100%, V₁₀, V₉₀ and V_(sat) having rangesof from 0->100V, wherein, in one embodiment, T_(max) has a range of from80˜100%, T_(min) has a range of from 0˜30%, V₁₀ has a range of from0˜5V, V₉₀ has a range of from 5˜20 V, Absorption_(on) has a range offrom 0.05˜0.10, and Absorption_(off) has a range of from 0.90˜1.00.

In a seventh aspect the object of the present invention is solved by adevice containing a composite according to the present invention.

In one embodiment, the device is characterized by the followingfeatures: T_(max) and T_(min) having ranges of from 0-100%, V₁₀, V₉₀ andV_(sat) having ranges of from 0->100V, wherein, preferably, T_(max) hasa range of from 80˜100%, T_(min) has a range of from 0˜30%, V₁₀ has arange of from 0˜5V, V₉₀ has a range of from 5˜20 V, Absorption_(on) hasa range of from 0.05˜0.10, and Absorption_(off) has a range of from0.90˜1.00.

In an eighth aspect, the object is solved by the use of a device or of acomposite according to the present invention in a display, a smartwindow, a membrane, an optical valve, a Bragg grating, an opticallysensitive memory, an infrared shutter, a gas flow sensor, a pressuresensor and/or a polarizer.

In a ninth aspect, the object is also solved by a method of forming acomposite containing at least one solid polymer component and at leastone liquid crystal component, comprising the following steps:

-   a) providing a material, capable of forming a solid polymer,-   b) providing a liquid crystal material,-   c) mixing the material, capable of forming a solid polymer, and the    liquid crystal material, to form a mixture,-   d) inducing the material, capable of forming a solid polymer, to    form the at least one solid polymer component,-   e) removing the liquid crystal material from the mixture,-   f) adding a liquid crystal material to the mixture so as to make the    at least one liquid crystal component.

In one embodiment the liquid crystal material of step f) is different tothe liquid crystal material of step e).

In another embodiment the liquid crystal material of step f) is the sameas the liquid crystal material of step e).

It is preferred that in step e) the liquid crystal material is removedfrom the mixture by a process selected from the group comprising washingout, evaporation, suction.

Preferably in step f) the liquid crystal material is added to themixture by a process selected from imbibing the liquid crystal materialinto the solid polymer, flooding the solid polymer with the liquidcrystal material, immersing the solid polymer into the liquid crystalmaterial, capillary force filling the solid polymer under vacuum.

It is to be understood that the removal step and the addition step maybe serial or concomitant.

In one embodiment the material, capable of forming a solid polymer, isinduced in step d) to form the at least one solid polymer component bymeans of a phase change.

Preferably the phase change is from liquid to solid.

It is preferred that the phase change is brought about by evaporation ofa solvent, contained in the mixture.

In one preferred embodiment the additional steps are comprised:

-   ba) providing a solvent, and-   ca) admixing the solvent of ba) to the mixture.

Preferably the solvent, provided in ba) is capable of dissolving boththe material, capable of forming a solid polymer, and the liquid crystalmaterial.

In one embodiment the phase change is brought about by lowering thetemperature of the mixture.

In another embodiment the material, capable of forming a solid polymer,comprises polymer precursors selected from the group comprising monomersand oligomers.

Preferably the material, capable of forming a solid polymer, is inducedin step d) to form the at least one solid polymer component by means ofa polymerization reaction.

In one embodiment the liquid crystal material added in step f) comprisesa substance selected from dyes, compounds with permanent dipoles,rod-like structure materials and nanotubes.

Preferably the substance selected from dyes, compounds with permanentdipoles, rod-like structure materials and nanotubes is sensitive to acondition associated with solvent evaporation, lowering of thetemperature or the polymerization reaction according to the presentinvention.

Preferably the substance selected from dyes, compounds with permanentdipoles, rod-like structure materials and nanotubes is sensitive toUV-light.

Preferably, the composite after f) is heated above the isotropictemperature of the liquid crystal material of step f), wherein, morepreferably, the heating is above the isotropic temperature of the liquidcrystal material of step f), but below the decompositiontemperature/melting temperature of the at least one solid polymercomponent.

In a tenth aspect, the object of the present invention is also solved bya polymer dispersed liquid crystal composite, containing at least onesolid polymer component and at least one liquid crystal component,wherein the liquid crystal component is the result of a replacementstep. Preferably the replacement step has taken place after formation ofthe solid polymer component. In one embodiment, the matter that has beenreplaced, is a liquid, preferably a(nother) liquid crystal component

In one embodiment the liquid crystal component is the result of areplacement step of a liquid crystal component of the same type.

As used herein, the term “replacement” can mean a replacement overall,i.e. a complete replacement or a replacement in parts. For example, amatrix comprising undoped liquid crystal material may be soaked in thesame liquid crystal material except for that the “soaking” liquidcrystal material may contain additional solutes, e.g. dyes. As a resultof such a “replacement” process, the liquid crystal material containedin the matrix may still be the same, whereas the solute has diffusedinto the liquid crystal. It can, however, also mean replacement of onetype of material through another type of material. The term“replacement” should not be construed to only mean complete replacement.

As used herein, a material, capable of forming a solid polymer can beany material which has the capability of forming a solid polymer. Thiscan, e.g. be a material comprising monomers, oligomers, etc., or it canbe a polymer melt which will solidify and thereby form a solid polymer.It can also be a solution of a polymer, which will form a solid polymerupon evaporation of the solvent.

A “solid” polymer, as used herein, can be solid throughout, or it mayhave pores or interstitial spaces, or it may be a polymer gel or polymernetwork.

A polymer dispersed liquid crystal pre-composite, as used herein, ismeant to signify a polymer dispersed liquid crystal, prepared accordingto the prior art, hence a liquid crystal wherein no replacement of theliquid crystal material has taken place. A phase separation process ismeant to denote any process wherein two phases separate from each other.These two phases may have existed originally, or they may developed inthe course of the events. The terms thermally-induced phase separation(TIPS), solvent-induced phase separation (SIPS) andpolymerization-induced phase separation (PIPS) are used herein as theyare used for example in the prior art (cf. Bouteiller, L. et al., 1996,Crystals, vol. 21, No. 2, 157-174; or Doane et al., 1988, Mol. Cryst.Liq. Cryst., vol. 165, pp. 511-532; or Whitehad et al., 2000 Proc. SPIE,vol. 4107, pp. 189-197), which are incorporated by reference.

A “polymer precursor” may be any precursor which is able, either byitself or by means of other additives to form a polymer. One example forpolymer precursor is monomers, oligomers, etc. Polymer precursors may,however, also be a liquid polymer melt. In the practice of the inventionuseful polymer precursors are selected from the group comprisingurethanes, acrylates, esters, lactams, amides, siloxanes, aldehydes,phenols, anhydrides, epoxides, vinyls, alkenes, alkynes, styrenes, acidhalides, amines, anilines, phenylenes, heterocycles and aromatichydrocarbons. Precursors may, for example, also be halogenated, inparticular fluorinated. Examples of useful precursors are described inKitzerow, H-S, 1994, LIQ. CRYST., 16, 1-31, which is incorporated hereinby reference. Useful polymer precursors can also be obtained from a widevariety of commercial sources one of them being US company NorlandProduct Inc. One example for a useful polymer (precursor) for thepractice of the present invention is NOA65 obtainable from Norland.

In the practice of the invention useful liquid crystal materials aremanifold, and a wide variety can be commercially obtained from varioussources. For example the company Merck offers a wide range of liquidcrystal materials. Although by no means limited thereto, useful examplesin the practice of the present invention include liquid crystalcompounds selected from the group comprising cyanobiphenyls andsubstituted cyanobiphenyls. The liquid crystal material referred to as“E7” which is a mixture of various proportions of differentcyanobiphenyls is particularly useful; the choice of liquid crystalmaterial, of course, depends on the intended application and purpose.

By the appropriate choice of a liquid crystal material desiredproperties can be achieved. For example, as will be shown below, theliquid crystalline material that is used to refill the matrix (whichmatrix had been formed by polymerization) can be appropriately selectedso as to achieve a fast rise time response or a low V₉₀ and a reasonablehigh transmittance at zero volt (T₀), or a low V₉₀ as well as a low T₀,which would be highly desirable, if such a composite were to be used ina display device. Some examples for various possibilities are givenbelow in example 7.

Different mechanism and methods exist to induce the material, containingpolymer precursors, to undergo a polymerization reaction; these can, forexample, be induction by UV-light, a radical addition reaction, acondensation reaction etc.

In the present invention, where a liquid crystal material is referred toas “being the same” as another liquid crystal material, this is meant tomean that the former liquid crystal material either comprises physicallythe bulk of the same molecules of the latter liquid crystal material, orthe former liquid crystal material comprises the same chemical speciesas the latter liquid crystal material.

Where a liquid crystal material is referred to as “being different” toanother liquid crystal material, this may mean a different chemicalspecies or mixture, or it may signify that one of the two liquid crystalmaterials contains additional components in comparison with the(otherwise chemically identical) other liquid crystal material. Theseadditional components may be other solutes like dyes etc. that one wantsto transport into the composite (in which case they are included in thesecond liquid crystal material), or they may be unwanted solutes likeuncured monomers that one wants to transport out of the composite (inwhich case the second liquid crystal material is purer than the firstliquid crystal material containing these unwanted solutes.

In the practice of the present invention useful dyes may have additionalgroups which alter the colouring effect of the dye. These groups may beauxochrome groups, which alter the absorption spectral properties of thedye, such as NR₂, OR, COOH, SO₃H, CN. Examples of UV-sensitive dyes aredyes with azo-groups, or dyes which additionally have a permanent dipolemoment like MORPIP.

It has been surprisingly found that by the present invention it ispossible to prevent plasticizing of the polymer matrix and, inapplications, where it is desirable to include a dye into the liquidcrystal, to prevent the incorporation of liquid crystal and dye into thepolymer matrix. This is achieved by pre-making a polymer matrix andadding the (e.g. dye doped) liquid crystal into it. This allows forapplications with a higher colour contrast, and enables theincorporation of dyes and liquid crystal molecules, normally sensitiveto UV light. The invention is also particularly useful in cases where itwould be difficult to obtain a PDLC because no phase separation occurs.This may for example be the case where, for maximum transmission overwide viewing angles and maximum scattering, one wants to match theextraordinary/ordinary refractive indices of the polymer component andthe liquid crystal component, and therefore chooses the polymer and theliquid crystal material accordingly. This usually results in a“phase-inseparability” of the two components. Prior art PDLC techniqueis bound to fail in this case, whereas with the method according to thepresent invention, one can simply form the polymer composite in a firststep using any phase separable material, e.g. water, in order to allowfor pore formation. Thereafter the phase separable material is washedout and replaced with the desired liquid crystal material. Anotheradditional advantage is that the composite according to the presentinvention has a faster switch-off time thus allowing for faster refreshrates in display devices comprising the material.

The invention allows also for example the preparation of a PDLC preparedby photo curing of a liquid crystal/prepolymer composite, where dyes ofany type compatible with the liquid crystal phase can be incorporated,regardless of their photosensitivity to ultra-violet light. Furthermore,this material type shows an improvement in the “turn-off” time. Amongstother aspects, the invention therefore provides for an improved PDLCmaterial more suited to colour display applications.

In the following detailed description reference is made to the figures,wherein

FIG. 1 shows the washing out of the PDLC-component, including anylc-material contained as a solute in the solid polymer phase, by meansof acetone,

FIG. 2 shows that the contrast ratio of the dye doped sponge-like PDLC(D-SPDLC) was improved by almost twice compared to the conventional dyedoped liquid crystal (D-LC).

FIG. 3 shows the comparison for the switching times for a PDLC filmprepared by a conventional method without dye (PDLC) and for acomparable material of the inventive subject (SPDLC=sponge polymerdispersed liquid crystal). Over a range of applied voltages, thereduction in switch-off time is approximately a factor of three,

FIG. 4 shows a comparison of transmittance between a Dispersed PDLC(2.5% B2 90% DPDLC) with a Heilmeier liquid crystal (2.5% B2 LC) dopedto the same concentration of dye,

FIG. 5 shows a comparison of transmittance between a Sponge PDLC (2.5%B2 70% SPDLC) with a Heilmeier liquid crystal (2.5% B2 LC),

FIG. 6 shows a transmittance measurement of undoped PDLC and undopedSPDLC vs. Applied Peak to Peak Voltage,

FIG. 7 shows Rise Time Measurement of undoped PDLC and undoped SPDLC,

FIG. 8 shows Rise Time Variation with inverse electric field square forPDLC and SPDLC,

FIG. 9 shows Decay Time of undoped PDLC and undoped SPDLC.

The following examples are intended to describe the invention morespecifically by way of example and are not intended to limit the scopeor spirit of the invention.

Example 1

In one embodiment of the present invention, a dye-doped liquid crystalcomponent of the PDLC is incorporated after the photo curing stage hasbeen completed. The first stage in the preparation of the PDLC is thatof the formation of the voids within which the dye-doped liquid crystalwill reside. This is achieved by curing a homogeneous mixture ofun-doped liquid crystal and liquid prepolymer. As an example, a 60% byweight mixture of E7 liquid crystal and NOA65 (Norland Optical AdhesiveInc.) liquid prepolymer may be cured using UV light to give an initialPDLC medium with well controlled LC droplet size and distribution.Following curing, the LC component, including any LC material containedas a solute in the solid polymer phase, is washed out using, forexample, acetone (FIG. 1).

The voids remaining are then re-filled using dye-doped liquid crystal,forming a dye-doped sponge-like PDLC (S-PDLC). In a preferred example,the dye is a highly dipolar dye used for colouration of the PDLC and asa means to obtain faster “turn-on” time. Morpip is one such dye example.

The resulting PDLC material regardless of dye content exhibits a markedimprovement in optical density (FIG. 2) and reduction in the“switch-off” time due to increased anchoring by the matrix walls (FIG.3).

Typical values obtained according to the present invention (PDLC+2.5%B2) can be compared with a conventional Heilmeier liquid crystal(LC+2.5% B2) in the following table.

TABLE contrast ratio Absorption_(ON) Absorption_(OFF) A_(OFF)/A_(ON)PDLC + 2.5% B2 0.08 0.99 12.4 LC + 2.5% B2 0.07 0.52 7.4

Conventional PDLCs

Sample Fabrication

First, a polymer-LC mixture was prepared by mixing an equal volume ofthe UV curable polymer, NOA65, and a doped liquid crystal E7. Themixture was stirred using Teflon coating magnetic stirrer for at leastone hour in dark. A 10 μm empty glass cell with no alignment layer(KSSZ-10/B111PINTS from E.H.C. Co., Ltd., Japan) was filled with thesolution at 70° C. Immediately after filling, the cell was cooled to theroom temperature of 21° C., the cell was irradiated by means of UV light(360 nm, Spectroline, Model EN-180L/F, 230 V, 50 Hz, 0.17 A) at anintensity of 4.8 mW/cm².

This UV curing process initiates cross-linking of the polymer, makingliquid crystal insoluble in the polymer. The phase separated liquidcrystal forms droplets, they merge and grow bigger until thepolymerization of the matrix has progressed sufficiently to lock theirmorphology. This curing process could be observed under across-polarised microscope. It is known that as the UV initiatescross-linking of polymers chains, the liquid crystal phase separatesfrom them and merges to form bigger droplets. The size of the dropletscan be controlled by the speed of the curing process which can becontrolled by the intensity of the UV irradiation.

PDLCs with different morphologies of the droplet type could be made byvarying E7-NOA65 composition and curing conditions. When the liquidcrystal volume proportion to the polymer was 80 vol % (80% PDLC), theliquid crystal droplets were no longer spherical in shapes but deformed.When the liquid crystal proportion was increased to 90%, the enclosureof liquid crystal in polymer matrix disappeared, and the network ofpolymer was formed in liquid crystal matrix. When the 90% PDLC is curedfaster, the phase separated polymer does not have enough time to formnetworks, and the polymer droplets are formed. These latter two types ofPDLC are known as network type PDLC and polymer ball type PDLC.

Example 3 Novel PDLCs

To overcome the low contrast problem due to dye deterioration and dyetrapping, two new dichroic PDLC fabrication techniques were proposed.For convenience, the PDLCs made by the first method were named DispersedPDLC (DPDLC), and the second ones were named Sponge PDLC (SPDLC). Theirfabrication and properties are described below.

a) Dispersed PDLC

-   -   The first method involves forcing doped liquid crystal “in”, and        consequently pushing un-doped liquid crystal “out” from a        ready-made PDLC cell. This method may be applied only when the        liquid crystal phase in the PDLC is interconnected. For the        liquid crystal-polymer combination used in this work, the liquid        crystal proportion in the PDLC must be more than 80% to achieve        the continuous liquid crystal phase.    -   It turned out that in many instances there were polymer balls in        the nematic liquid crystal. The refilling process did not sweep        the polymer balls out from the cell, therefore they were        probably attached to either side of the substrates. In these        cases, the cell was made by curing 90% PDLC for 2 minutes with        the UV source placed 10 cm away from the cell.    -   Further, the transmittance of the DPDLC was compared with a        Heilmeier liquid crystal doped to same concentration of dye to        see how scattering has improved the absorption of the dye. The        result which can be seen in FIG. 4 showed a transmission        decrease at 800 nm, which indicates that more scattering was        present in DPDLC compared to Heilmeier liquid crystal. Even        though the DPDLC has 10% less dyes present compared to the        Heilmeier liquid crystal, the transmission at 550 nm stays the        same (54%), implying the increase in dye absorption due to        scattering. Unfortunately, the DPDLC contrast was 1.63        (T_(ON)/T_(OFF)=88%/54%) at 530 nm, which was still to weak for        display applications that requires at least a contrast of 2.7.        It was not possible to increase the contrast much more by using        the same liquid crystal (E7) and polymer (NOA65) combination, as        the mixture starts forming droplets under 80% PDLC. The network        type PDLC or polymer ball type PDLC, which has continuous liquid        crystal, with very high scattering would further improve the        contrast using the dispersion method.        b) Sponge PDLC (SPDLC) (or Sponge-Like PDLC)    -   This second new fabrication technique, which gives an increased        contrast compared to DPDLC introduced in the previous section,        makes use of the fact that E7 liquid crystal is highly soluble        in acetone, while NOA65 polymer is only slightly soluble. When a        ready-made undoped PDLC cell was soaked in acetone, E7 liquid        crystal and uncured monomer and oligomer in the PDLC cell slowly        dissolve in the solution.    -   The cell became less scattering when E7 mixes with acetone, but        it became weakly scattering again as the E7 is fully washed out.        The duration of this process depends on the size and proportion        of liquid crystal droplets. When the droplet sizes are in order        of 1 μm, and the liquid crystal proportion is 50%, the washing        process takes a few weeks. If the droplet sizes are in order of        100 μm, and the liquid crystal proportion is 90%, i.e. all the        liquid crystal is connected together, the process takes only a        few days.    -   After fully removing the E7, slow heating in the drying cabinet        evaporated the acetone in the remaining acetone-polymer system.        A sponge of polymer matrix with air cavities remained.        Observation of the polymer sponge under a microscope did not        show any noticeable difference in the matrix structure.    -   Then the cell was stood upright in a small beaker filled with        desired dye doped liquid crystal, leaving one open-end of the        cell not soaked in the liquid crystal. Then the beaker was        quickly placed in a vacuum oven at 40° C. This refilling method        in vacuum avoids any air left in the matrix after filled by        doped liquid crystal. Finally, when the cell is refilled, it was        taken out of the beaker, and both open-ends of the cell were        sealed with epoxy.

Example 4 Contrast Measurement

Off-state transmittance of doped SPDLC and a conventional Heilmeierliquid crystal cells were compared to investigate the contrastimprovement which could not be observed with doped PDLC. Both cellscontained 2.5 wt % B2 in the liquid crystal. The liquid crystalproportion to polymer in SPDLC was 70%. B2 is a mixture of azo andanthraquinone dyes commercially available from Mitshubishi Chemical inJapan.

The result in FIG. 5 shows that the Heilmeier liquid crystaltransmittance of 55% was decreased to 30% less liquid crystal, and hence30% less dyes. At 520 nm, doped SPDLC achieved a contrast of 3.0compared to 1.7 for the Heilmeier liquid crystal. The decrease intransmittance was clearly achieved by the scattering effect, as can beobserved by the decrease of transmittance at 800 nm where there is noabsorption by the dye. The effect of the scattering can be seen by afurther decrease in the SPDLC transmittance at 400 nm. This is becausethe scattering efficiency decreases rapidly with increasing wavelength.

Example 5 Threshold Characteristic of SPDLC

Following the successful contrast result from the previous example theSPDLCs were investigated further by comparing the electro-opticproperties of undoped SPDLC with undoped PDLC. Two identical undopedPDLC cells were made under the same conditions. The liquid crystalproportion of the PDLC's was 60%, and the cells were irradiated with UVfrom 10 cm away for 2 minutes. Both cells were 10 μm thick without anyprior alignment treatment. Then one of these cells was converted to anundoped SPDLC sample by the following method. The E7 was simply washedaway and the polymer sponge was filled with undoped pure E7 liquidcrystal. Transmittance variation with applied voltage was measured andthe result shown in FIG. 6 was obtained.

The result shows that the V₁₀ is 2.5±0.3 V for PDLC, and 3.5±0.3 V forSPDLC. V₉₀ for PDLC is 7.5±0.3 V and 12±0.3 V for SPDLC. Both V₁₀ andV₉₀ were increased by approximately 34% by transforming the PDLC intoSPDLC. The increase indicates increase in anchoring energy at thepolymer walls, caused by the removal of the uncured monomer and oligomeror drying, or combination of both.

The values for T_(max), T_(min), V₁₀, V₉₀, V_(sat) are dependent on thesample and the cure conditions and vary from 0˜100% (T_(max), T_(min)),and from 0˜>100 V (V₁₀, V₉₀, V_(sat)).

Typical values obtained according to the present invention are T_(max)80˜100%, T_(min) 0˜30%, V₁₀ 0˜5V, V₉₀ 5˜20V; these values can, forexample, be obtained from a composite comprising 60% E7 and 40% NOA65,where the thickness is 10 micron.

Example 6 Response Time Measurement

To further characterize the SPDCL, the response times of undoped PDLCand undoped SPDLC were measured using the same set-up used in theprevious example. All cells tested were 10 μm thick without any surfacealignment. Rise and decay time results are shown in FIG. 7 and FIG. 9respectively.

The inconsistent variation at lower voltage, under 8V, was due to theliquid crystal not reaching full alignment. Nevertheless, the trend ofundoped SPDLC responding slower to the electric field compared toundoped PDLC can be seen when higher voltages are applied. Thisdifference shown more clearly when the rise time variation with inversesquare of the electric field is plotted as shown in FIG. 8. Assumingthat the PDLC behaves to electric field as liquid crystal does, astraight line through the origin was fitted to the data points, and thegradient calculated. The gradients of the PDLC and SPDLC samples were0.016±0.002 sV² μm⁻² and 0.031±0.002 sV² μm⁻² respectively. Even thoughthe lines were not fit perfectly, the difference in gradients clearlyindicates that the SPDLC is approximately twice as slow as the PDLC.Nevertheless, they are both within the targeted range of 100 ms under anapplied filed of 10 Vm.

The same PDLC and SPDLC cells were used to measure decay time, and theresult is shown in FIG. 9. Surprisingly, the decay time of the SPDLCcell is only 73% of the decay time obtained for the PDLC cell. The SPDLCcell switches off as fast as it switches on, and this can be usefulsince the slow decay time of liquid crystals is one of the problemssuffered by liquid crystal displays. The measured decay time for 10 μmHeilmeier liquid crystal was 250 ms, which is considerably longer thanthe 30 ms for SPDLC.

Increases in the rise time and decreases in the decay time, togetherwith the increased threshold voltage measurement from the previoussection, are common effects observed when the anchoring energy of thepolymer wall is increased. Further measurements of anchoring energywould reveal the effect.

Example 7

SPDLC properties can be tuned to give desired properties by selecting anappropriate liquid crystal (LC) for the refilling (i.e. the second LCcan be different from the LC which was first used to make the PDLC). ThePDLCs used in the following were made by polymerization of PN393 in thepresence of TL213. PN393 is an acrylate based UV curable polymer and isavailable from Merck. TL213 is a liquid crystalline material and isavailable from Merck. The table shows the properties of TL213-PN393SPDLC cells refilled with three different nematic LCs available fromMerck (TL213, TL203 and 5CB). For example, one can refill the SPDLCsponge with 5CB if it is desirable to have a fast rise time responsewhile the degree of scattering at 0V is not important, i.e. T₀ can behigh. On the other hand, TL203 might be selected if one requires a lowV₉₀ while not sacrificing the transmittance (T₀) much. An LC used forrefilling which decreases V₉₀ as well as T₀, is highly desirable forSPDLCs used in display devices.

TABLE Contrast Ratio V₉₀ Rise time Decay time T₀ T100 [T₁₀₀/T₀] [V] [ms][ms] [%] [%] TL213 4.077 8.6 96.5 198.02 19.49 79.49 TL203 0.276 7.8524.45 101.97 27.85 85.15 5CB 1.591 4.05 1.36 354.76 56.36 89.69

Furthermore, it is also possible to further modify the properties of theSPDLC cells by adding a dichroic dye to the liquid crystal material thatis used for refilling. In doing so, i.e. in using an absorbing dye-dopedliquid crystal material for refilling, it is possible to achieve acolour-transparent test cell, i.e. a test cell that switches between aspecific coloured state (depending on the (dichroic) dye used) to atransparent state. For the fabrication of such a colour-transparent testcell, it is important that the polymer matrix that is refilled with theliquid crystal material containing the dye, has a refractive index whichis closed to or matching the refractive index of the liquid crystal.After the refilling of the filter with the liquid crystal material(containing the dye) it may be necessary to heat the cell above theliquid crystal's isotropic temperature and cool it again. Thetemperature however, must not exceed the decompositiontemperature/melting temperature of the polymer matrix wherein the liquidcrystal material was refilled.

In general, such a heating step should be performed for 1-20 minutes,preferably 1-10 minutes, more preferably 1-5 minutes, and the coolingshould be performed over a period of 1-60 minutes, preferably 1-40minutes, more preferably 5-20 minutes.

Example 8

In summary, the previous examples have shown the following:

The conventional PDLCs were made successfully using the UV initiatedphase separation method. Other morphologies, such as polymer networktype and polymer droplet type PDLC, could also be made by varying theproportion of liquid crystal to the polymer. Although these morphologieswere interesting in themselves, they did not scatter sufficiently. Theliquid crystal proportion of 50% with rapid curing provided the mostscattering PDLC.

While measuring the optimum time needed for the PDLC curing, the dopedPDLCs required far longer, as much as four times, the cure time requiredfor the undoped PDLC. The reason was believed to be the UV absorption bydye, preventing the polymer curing. Also the deterioration of dyes wasencountered for light sensitive dyes.

Nevertheless, the cure time required for MORPIP doped PDLC was the sameas undoped PDLC, implying that the morphologies, such as droplet size,change were minimal by the MORPIP doping. Indeed, no observable changein droplet size and morphologies could be seen under the cross polarisedmicroscope. Hence the response time of the PDLCs with differentconcentrations of MORPIP could be compared. The result showed that therise time decreases with increasing concentration of MORPIP 45% decreasein rise time was recorded with 0.37 wt % of MORPIP. One of possiblereasons for a difference in the rise time compared to the 21% decreaseof the simple GH liquid crystal is the slight increase in droplet sizeMORPIP has some absorption at 360 nm, making the cure time required forMORPIP doped PDLC slightly longer and hence making the droplet sizebigger than the undoped PDLC. The anchoring energy of such MORPIP dopedPDLC is smaller, and consequently contributing to the further decreaseof the rise time.

The contrast measurement of the doped PDLCs showed an insufficientcontrast. The sources of the problems were determined as poor off-statescattering due to long cure time, and poor on-state transmittance due tothe dyes trapped in the polymer matrix. The poor off-state scatteringcould be solved by using chemical accelerator to increase the curingspeed. The poor on-state transmittance could be solved by chemicalsynthesis of dyes and liquid crystal who are insoluble to the polymermatrix. Otherwise different fabrication techniques of PDLC such as NCAPsystems seem to produce better results.

Nevertheless conventional PDLCs of the prior art and, as an example ofthe invention, two new fabrication methods were proposed to overcome allthe problems of long curing dye trapping as well as dye deterioration.

The first fabrication method was named Dispersed PDLC (DPDLC). Itinvolves forcing doped liquid crystal “in”, and consequently pushingundoped liquid crystal “out” from a ready-made PDLC cell. The techniqueavoided the exposure of dyes to UV as well as trapping of dyes. Themethod was simple, and it proved to increase dye absorption by increasein scattering. However, this method could be only applied when a liquidcrystal droplets are interconnected to each other, and it was notpossible to fabricate a high scattering network type PDLC with E7-NOA65combination. It is possible to obtain a contrast 3 times as large asthat of the droplet type PDLC thus application of the method to a highscattering polymer network of ball type PDLC would further improve thecontrast of DPDLC.

The second fabrication method was named Sponge PDLC (SPDLC) (or“sponge-like polymer dispersed liquid crystal”). It involves washing outthe liquid crystal “out” from undoped PDLC to make a sponge of polymer,and forcing the doped liquid crystal “in” to the open porous polymer.This method allowed the use of more scattering 50% PDLC, achieving thehigher contrast of 3 compared to any of the dichroic PDLC made in thisstudy. The preliminary results showed that undoped SPDLC has 34%increased threshold voltage of 12V, 100% longer rise time of 30 ms, but73% shorter decay time of 30 ms compared to the conventional PDLC.Although the threshold voltage and rise time were slightly increased,the considerably shorter decay time would be useful for the display. Theonly disadvantage of the SPDLC was its slow fabrication owing to thediffusion of acetone into PDLC. Nevertheless, there is a scope forimprovement in the fabrication speed by 1) modifying the diffusionprocess, 2) using different materials, and 3) using different polymermatrix structures.

By appropriate choice of liquid crystal materials it is possible tofine-tune the properties of SPDLCs.

The features disclosed in the specification, the claims and the drawingsmay, alone or in any combination thereof, be essential in the practiceof the present invention.

1. A composite comprising a matrix component and at least one liquidcrystal component, obtainable by a method comprising: providing amatrix; providing a first material that is phase separable from thematrix; adding the first material to the matrix; removing the firstmaterial that is phase separable from the matrix; and adding a secondmaterial that exhibits liquid crystalline behavior to the matrix afterremoving the first material such that the second material replaces thefirst material, wherein the matrix component is a solid polymer withoutdyes trapped.
 2. The composite according to claim 1, wherein the atleast one liquid crystal component is doped with a compound selectedfrom a group consisting of UV-sensitive dyes, UV-stable dyes, dichroicdyes, and dyes with a permanent dipole, rod-like structure material, andnanotubes.
 3. The composite according to claim 1, wherein Tmax and Tminof the composite range from 0-100%, and V10, V90, and Vsat of thecomposite range from 0->100V.
 4. The composite according to claim 3,wherein the Tmax ranges from 80-100%, the Tmin ranges from 0-30%, theV10 ranges from 0-5V, the V90 ranges from 5-20V, Absorption_(on) of thecomposite ranges from 0.05-0.10, Absorption_(off) of the compositeranges from 0.90-1.00, and a contrast ratio AOFF/AON of the compositeranges from 6-20.
 5. A device, comprising: the composite according toclaim
 1. 6. The device according to claim 5, wherein Tmax and Tmin ofthe composite range from 0-100%, and V10, V90, and Vsat of the compositerange from 0->100V.
 7. The device according to claim 6, wherein the Tmaxranges from 80-100%, the Tmin ranges from 0-30%, the V10 ranges from0-5V, the V90 ranges from 5-20V, Absorption_(on) of the composite rangesfrom 0.05-0.10, and Absorption_(off) of the composite ranges from0.90-1.00.
 8. An apparatus, comprising: the device according to claim 5,wherein the apparatus is one of a display, a smart window, a membrane,an optical valve, a Bragg grating, an optically sensitive memory, aninfrared shutter, a gas flow sensor, a pressure sensor, and a polarizer.9. An apparatus, comprising: the composite according to claim 1, whereinthe apparatus is one of a display, a smart window, a membrane, anoptical valve, a Bragg grating, an optically sensitive memory, aninfrared shutter, a gas flow sensor, a pressure sensor, and a polarizer.10. The composite according to claim 1, wherein the first materialexhibits liquid crystalline behavior.
 11. The composite according toclaim 1, wherein the first material is liquid.
 12. The compositeaccording to claim 11, wherein the first material is selected from thegroup consisting of water, aqueous solutions, aqueous suspensions,aqueous emulsions and oils.
 13. The composite according to claim 10,wherein the first material exhibiting liquid crystalline behavior is thesame as the second material exhibiting liquid crystalline behavior. 14.The composite according to claim 10, wherein the first materialexhibiting liquid crystalline behavior is different from the secondmaterial exhibiting liquid crystalline behavior.
 15. The compositeaccording to claim 1, wherein the second material exhibiting liquidcrystalline behavior contains at least one additional component.
 16. Thecomposite according to claim 15, wherein the at least one additionalcomponent is soluble in the second material.
 17. The composite accordingto claim 16, wherein the soluble component is selected from the groupconsisting of dyes, compounds with permanent dipoles, rod-like structurematerials, and nanotubes.
 18. The composite according to claim 17,wherein the soluble component is a dye selected from the groupconsisting of UV-sensitive dyes, UV-stable dyes, cis-trans isomer dyes,dichroic dyes and dipolar dyes.
 19. The composite according to claim 1,wherein the at least one liquid crystal component is doped with a dye.